1. Field of the Invention
This invention relates to a data processing apparatus for a camera provided with a microcomputer comprising a central processing unit (CPU) and a memory device.
2. Description of the Prior Art
The use of a microcomputer in a control circuit for controlling the shutter circuit, the aperture circuit, the photometering circuit, the automatic focus detecting circuit, the sensor circuit, the display circuit, etc. of a camera is known. The microcomputer comprises a central processing unit and a memory device in which are stored a program for the control and data necessary for the execution thereof. The microcomputer and the various surrounding circuits are connected by a data bus, and exchange of data is effected therebetween by control signals. The central processing unit effects predetermined data processing on the data stored in the memory device and the measurement data from the surrounding circuits, in accordance with the predetermined program stored in the memory device, and delivers control signals and data corresponding to the result thereof to the surrounding circuits, to thereby control these surrounding circuits.
A random access memory (RAM), a fixed value memory (ROM) and an electrically erasable programmable fixed value memory (EEPROM) are known as memory devices comprising semiconductors, and they have their own merits and disadvantages. A RAM is capable of rewriting data at any time, but it always requires a back-up power source for the retension of data and loses its memory contents when the power source is cut off and thus, it is not suitable for the control of a camera. A ROM does not require a back-up power source and is excellent for data preservation, but it is not capable of rewriting data, and data are usually written en bloc into it during the manufacture thereof as a mask ROM and therefore, discrete data matching the characteristics of individual cameras cannot be written into a ROM. An EEPROM has the merits of RAM and ROM and does not require a back-up power source for the retension of data and is capable of electrically rewriting data, but it is inferior in data preservation to ROM. Accordingly, EEPROM is poor in reliability for its use as a control device which is incorporated into the camera and thereafter must retain data for a long time, and it is not free from the possibility of losing data.